At issue is Ford's claim in mid-July that a 2015 F-450 4x4 Crew Cab pickup can tow 31,200 pounds.

That is 1,200 pounds -- about the weight of a good-sized horse -- more than the Ram 3500's highest towing capacity of 30,000 pounds in a 4x2 Regular Cab pickup. So Ford claims the "best-in-class" towing crown for heavy-duty pickups.

But it's not that simple, thanks in part to the way Ford calculates maximum payload.

Ram says the F-450 and the Ram 3500 aren't in the same class. It says the F-450 is a larger, Class 4 pickup -- in fact, the only Class 4 pickup offered by any automaker.

The dispute may seem like just a marketing tug-of-war, but the stakes couldn't be higher. Towing capability is among the top reasons buyers purchase heavy-duty pickups, automakers say. And heavy-duty pickups represent 23 percent of total pickup sales in the United States through June, according to TrueCar.com.

At an average transaction price north of $50,000 for each pickup, billions of dollars in sales are on the line.

Class question

Truck classes are defined by the Department of Transportation's Federal Highway Administration. In total, there are eight classes, separated by weight, that cover everything from a Class 1 Toyota Tacoma up to Class 8 tractor-trailer rigs.

Almost all pickups fall within the first three classes, with what the government calls a "gross vehicle weight rating" -- the base curb weight of the vehicle plus its maximum payload -- of no more than 14,000 pounds. Go one pound over those seven tons, and the vehicle moves to Class 4.

Ford says its 2015 F-450 has a gross vehicle weight rating of 14,000 pounds and is therefore a Class 3 truck. Ford says the F-450 is similar to the F-350 but "with a stronger F-350 frame, suspension, and 19.5-inch wheels and tires from the F-450 chassis cab."

In a statement sent to Automotive News, Ram said it disagrees with Ford's assertion that the F-450 is a Class 3 truck and will stick to its marketing guns.

Ram also took a shot at Ford for making its towing claim even though Ford acknowledges that it uses its own rating system, not the commonly accepted measurement standard known as SAE J2807.

"Our best-in-class claim of 30,000 pounds of towing capacity for the 2014 Ram 3500 stands firm in the 350/3500 segment.

Additionally, unlike our competitors, our new 2015 Ram 3500 will hold the title and weight capacity while adhering to the SAE J2807 towing test criteria," Ram's written statement said.

The claims involve fifth-wheel or gooseneck towing, in which the trailer is connected in the pickup bed. Ford says it will follow the J2807 towing standard as it redesigns its F-series pickups, beginning with the 2015 F-150.

Weights, measures

After a media event Ford held in mid-July touting the F-450's towing claim, some analysts -- and a great number of online comments -- disagreed that the F-450 is in the same class as the F-350.

"That is a Class 4 truck under the skin," said Dave Sullivan, manager of product analysis for AutoPacific. "It has all the equipment of all of their Class 4 trucks. They call it the F-450, not F-350. This has significant hardware changes to Ford's own Class 3 Super Duty. That's what puts it into the next class," regardless of the gross vehicle weight rating.

The thorny issue is complicated by the method Ford uses to determine the maximum payload of all its F-series pickups.

Ford says the F-450 has a base curb weight of 8,611 pounds and a maximum payload of 5,450 pounds. Add them up, and it comes to 14,061 pounds -- 61 pounds over the 14,000 limit to keep it a Class 3 pickup.

A Ford spokesman insists, though, that the F-450's gross vehicle weight rating is 14,000 pounds. He explained that Ford bases its maximum payload claim not on the base curb weight, as Chrysler does, but on the weight of the base vehicle after various items are deleted from a base F-450.

Ford shaved 154 pounds from the weight of the F-450, he said, by removing items that have the possibility of being deleted from a vehicle order. Among the items removed were the spare tire, tire jack, radio and center console.

Ford said it uses this practice to set the maximum payloads for all F-series pickups.

By comparison, General Motors has based its maximum payloads on the lightest version of a pickup a customer can order from its order book, including a heavy-duty pickup without a rear bumper. That minimum curb weight is below the weight of the lightest base version.

For the 2015 model year, the weight of the spare tire will also be subtracted to calculate the lightest vehicle configuration for the light-duty pickups, a spokesman said.

Sitting out

GM touts the pulling prowess with conventional towing, in which a trailer is connected below the rear bumper.

Tom Wilkinson, a spokesman for GM's pickup lines, said the automaker won't engage in a towing arms race "that is meaningless to 99.9 percent of customers" and will instead focus on "capability and confidence while towing."

Wilkinson said the average heavy-duty customer tows about 9,000 pounds, giving consumers a wide choice of heavy haulers. GM has instead focused on integrating cruise control, powertrain grade braking and its diesel exhaust brake to make it easier to climb and descend steep grades while towing.

"As long as the specs meet your needs, the other stuff is what really counts," Wilkinson said. GM plans to comply with the J2807 towing standard for its heavy-duty pickup ratings for the 2016 model year, Wilkinson said.

GM may be about to up its own heavy-duty diesel game, however. Spy photographers in July caught camouflaged GM heavy-duty pickups doing hot-weather testing in the California desert.

The big pickups were diesel-powered, likely testing upgraded versions of the 6.6-liter Duramax turbodiesel with a new, large, cool air intake along the front edge of the hood.